This invention relates to the transfer of toxic or radioactive materials. In plants utilising such materials it is known to perform any work on the materials inside enclosures which are isolated from the environment. An example of such an enclosure is a glove box in which all operations are performed by an operator outside the glove box using gloves attached to appropriate positions in the walls of the box. The use of these enclosures is intended to ensure that none of the toxic or radioactive material is dispersed into the environment around the enclosure. It is particularly important that no dispersal occurs during the transfer of materials into and out of the enclosure.
Several methods of obviating the problems of dispersal during the transfer of materials into and out of enclosures have been proposed in which the so-called "double-cover" principle is employed. In these systems the material is transferred into or out of a container through a port in the wall of the enclosure, the container being attached to the wall of the enclosure around the port which is normally closed by a port cover. In the "double-cover" principle any part of the port or container which is exposed to the environment when the container is separated from the port is protected from exposure to the atmosphere within the enclosure. In one known method the port cover and the container cover are engaged as the container is fitted around the port so that their outer surfaces face each other and a seal is provided to prevent contamination of the outer surfaces when the interengaged covers are inside the enclosure. The seals used are complex in shape and expensive to produce and may produce a ring of contamination on their sealing surface which may be dispersed when the container is removed from the port.